1. Field of the Invention
The present invention relates to a thermoelectric material, a thermoelectric conversion module and a thermoelectric power generating device using the same.
2. Description of the Related Art
In recent years, with rising consciousness about the global environmental issues and the like, there has been growing interest in thermoelectric cooling devices using the Peltier effect, which are CFC-free refrigerators. Similarly, from the viewpoint of reduction in exhaust amount of carbon dioxide, and effective use of energy, there has been growing interest in thermoelectric power generating devices using the Seebeck effect, as a power generating system using unused waste heat energy. These thermoelectric conversion devices include a thermoelectric conversion module in which p-type and n-type thermoelectric materials are alternately connected in series.
As the thermoelectric material, a Bi—Te type single crystal or poly crystal are frequently used in the devices used at around a room temperature. When a thermoelectric conversion module is manufactured, both p-type and n-type materials are constituted of Bi—Te type materials. The n-type material is generally doped with Se. For a thermoelectric material used at a temperature higher than a room temperature, a Pb—Te type material is used because of high efficiency.
The Bi—Te type and Pb—Te type thermoelectric materials include Se (selenium), Pb (lead) and Te (tellurium) which are toxic and harmful to humans, and these are also unfavorable substances from the viewpoint of the global environmental issues. Therefore, thermoelectric materials which are substituted for Bi—Te type and Pb—Te type materials are demanded. In this respect, a material including a phase having an MgAgAs crystal structure (hereinafter, described as an MgAgAs crystal phase) as a main phase (hereinafter, called a Half-Heusler material) attracts attention (see JP-A 2005-116746 (KOKAI)).
Among Half-Heusler materials, (Ti, Hf, Zr)—Co—Sb type materials obtain high thermoelectric characteristics, and are promising as thermoelectric materials. However, the (Ti, Hf, Zr)—Co—Sb type materials include a large amount of Sb (antimony) though they hardly include Se, Pb and Te. Sb is also toxic and harmful to humans, and therefore, reduction in the use amount of Sb is demanded. Thus, reduction in Sb amount without impairment of high thermoelectric characteristics of the (Ti, Hf, Zr)—Co—Sb materials is demanded.